Piezoelectric crystal apparatus



W. P. MASON PIEZOELECTRIC CRYSTAL APPARATUS June 7, 1949.

2 Sheets-Sheet 1 Filed Aug. '16, 1946 ETHYLE/VE D/AMl/VE TZRTRATE CRYS 771L$ FIG. 3 Lowe/mum M005 INVENTOR ml? MASON ATTORNEY June 7, 1949.

w. P. MASON PIEZQELECTRIC CRYSTAL APPARATUS 2 Sheets-Sheet Filed Aug. 16, 1946- FIG. 4 LONGIMINAL MODE war -40 -go o rim/MIME:

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x/vvnvraq W P MASON ATTORNEY Patented June 7, 1949 UNITED STATES PATIENT OFFICE PIEZOELECTRIC CRYSTAL APPARATUS 'Warren'P."Mas0n, West Orangc,N. .1., assignor-to *Bell 'lelephone Laboratories, Incorporated, New

*lZork, N. Y., a-corporation: of New York ApplicationAugustlG, 1946,.Serial No. 690,872

ll claims. .1

This invention relatestocrystal apparatus and particularly to piezoelectric crystalelements comprising ethylene diamine tartrate (CsHmNzOs). Such crystal elements may be usedas frequency controlling. circuit elements in electric Wave filter systems, oscillatiomgenerator systems andamplifier systems. Also, they may be utilized as modulators, or as harmonic producers, -or as electromechanical transducers in sonic or supersonic projectors, microphones, pick-up devices and detectors.

One of theobjects of this inventionis to-pro- .vide advantageous orientations in crystal elements made from synthetic crystalline ethylene diamine tartrate.

Another object of this invention is to 'takead- .vantageof the high piezoelectric coupling, the low ratio of capacities, the low cost and other advantages of crystalline ethylene diamine tartrate.

Other objectsof this invention are toprovide .crystal elements comprising ethylene diamine tartrate that maypossess useful characteristics, such as effective piezoelectric constants, min- .imum or, low coupling of the desired mode of motion to undesired modes of motion therein, and low orl-zero temperature r,coelllcient offrequency.

A particular object of this invention is to provide synthetic ethylene diamine tartrate crystal elements having a zero temperature coefiicient of frequency.

.Other objects of thisinvention are to Provide cuts of the double orientation type in ethylene diamine tartrate crystals which may have a flat- ,ter temperature-frequency characteristic curve,

which may have a higher impedanceqor greater ratio of capacities, and which may have mechanically stronger surfaces for purposes of cementing or otherwise securingsupporting wires thereto.

Ethylene; diamine tartrate isa salt of tartaric acid having a molecule which lacks symmetry elements. In its-crystalline form, it lacks a center-of symmetry and belongs to a crystal class which is piezoelectric and which is the monoclinic .sphenoidal crystal class. By virtue of its struc- .-ture, ethylene diamine tartrate will form crystals offering'relatively high piezoelectric constants. In addition, the crystalline material-.afiords certaingcuts with low or zero temperature-coefficient of .vibrational frequency and low coupling to other modes ,ofcmotion therein, and fairly. high Q or: low dielectric loss and :mechanical dissipation. Also crystalline ethylene fdiamine tartrate-has.- no

2 water of crystallization and-henceWillnot dehyclrate when used in air or in v acuum.

Crystal elements of suitable orientation cut from crystalline ethylene diamine tartratemay be excited in diiferentmodes-of motion such ias the longitudinal lengthor the-longitudinal width modes oflnotion. Also, -low frequencyfiexural modes of motion of either the widthbendi-ng fiexure type or the thickness bendingflexure cluplex ;type maybe obtained. These variousmodes of'motion are similar in thegeneralform-of their motion to those of similar or corresponding names that are already'known-in connection with crystal elements cut-from other crystalline substances such as quartz, Rochelle salt and ammonium dihydrogen phosphate crystals, for example.

It-is useful to havea synthetic type 'of piezoelectric crystal element having a lower zero temperature coefficient of frequency, and having ..a low coupling to other modes 'of'motiontherein. In accordance with this invention, such synthetic type crystal cuts may Joe -provided in-theform of ethylene diaminetartrate crystals and suchetartrate crystals may be suitablecuts taken 'from crystalline ethylene-diamine tartrate adapted to operate in;a suitable mode-of motion. Such zero crystal elements having their major faces and major plane section disposed perpendicular or nearly perpendicular "with respect tothe' Y or--b axis and operatingin the longitudinal -mode of motion along-the longest or lengthwise axis dimension thereofithe leng-thaxis dimension being disposed or inclined at-ananglein-theregion =frqm-0-to $25 degreeswith-respect to the +X axis; or in the -reg-ion=of=0:- degrees where a-zero temperature coefficient of*frequencyis -desired-at ordinary -room temperatures in the region-of about +27 degrees centigrade. -The.temperature at which the zero temperature coefficient occurs for the longitudinal lengthaxis mode of motion varies according to the value of the angle selected, and is at about +27 :degrees centigrade for-tan angle of. about .0. degrees,.:at ,about +20. .'degre.es

and at -values between e40 degrees t; and .-}7:27

degrees centigrade for values of angles between and -20 degrees. The coupling of the longitudinal length axis mode of motion to other modes of motion therein is small, and at the angle of about 0 degrees, there is no face shear mode of motion in the crystal element. That Y-cut longitudinal mode crystal element, when its length axis dimension is disposed along the X axis, has a ratio of capacities of about 27, a frequency-curvature constant a2 of about 1.4 10 and a change of inductance of about $3 per cent from 55 degrees Fahrenheit to 110 degrees Fahrenheit, which is the usual ambient temperature range that crystal filters have to meet in practice.

As compared with such Y-cut longitudinal mode crystal elements disclosed and claimed in the earlier Mason application Serial No. 657,886 referred to, the longitudinal mode ethylene diamine tartrate crystal cuts provided in accordance with the presentinvention have relatively flatter temperature-frequency characteristics, less variation of inductance with temperature change, and higher impedance, and may be used as a direct replacement of quartz filter crystals in carrier systems utilizing filters such as channel filters and pilot pick-01f filters. Moreover, due to freedom from fracture or cleavage plane effect along the mountin surfaces, the cuts provided in accordance with this invention, may have stronger surfaces for cementing purposes. The crystal elements may be defined as to orientation by the angles i and 0. The temperature at which the zero temperature coefficient of frequency occurs varies with the value of the angle 0 and occurs at about 27.5 degrees centigrade when the angle 0 is about 63 degrees, the angle I being 45 degrees or in the region of 45 degrees. For a I angle of about 45 degrees and a 6 angle of about 63 degrees, the ratio of capacities is about 35 at a temperature of about 25 degrees centigrade, the curvature constant a2 is about 0.75 10- and the Variation of inductance over the temperature range from 55 degrees Fahrenheit to 110 degrees Fahrenheit is about per cent. The frequency spectrum is such that all prominent resonances may be separated from the main longitudinal mode along the length axis dimension by a factor of about 2 to 1 when the dimensional ratio of the width with respect to the length is less than about 0.3 to 0.5.

The synthetic tartrate crystal elements provided in accordance with this invention have a high electromechanical coupling which isof the order of 20 to 25 per cent, a high reactance-resistance ratio Q at resonance, and a small change in frequency over a wide temperature range. These advantageous properties together with the low cost and freedom from supply troubles indicate that these crystal elements may be used in place of quartz as circuit elements in crystal filters and oscillators. Moreover, since the high electromechanical coupling existing in these crystals allows the circuit frequency to be varied in much larger amounts by a reactance tube, than can be done for the frequency of crystal quartz, such tartrate crystal cuts may be advantageously used for frequency modulating an oscillation generator.

The tartrate crystal elements provided in accordance with this invention may be especially useful in filter systems, for example. When used in channel filters, for example, the electromechanical coupling in these crystal elements is so high that regular channel widths of about 3600 cycles per second, for example, may be obtained without the use of auxiliary coils for frequencies as low as 60 to kilocycles per second, for example. Accordingly, such a crystal channel filter may be produced more cheaply and put into a smaller space than one which is used with bulky and expensive coils and condensers. When such crystal filters are to be paralleled, a terminating network comprising coils and condensers may be used therewith in order to obtain no paralleling loss; or terminating resistances may be used therewith and the paralleling loss made up for by an added stage of amplification. The tartrate crystal elements in accordance with this invention have a low ratio of capacities and accordingly may be used in wide band filters, such as, for example, in program filters where the tartrate type crystal element may be used to control the loss peaks located at some distance from the passband, while using quartz crystals if desired for the sharpest peaks nearest the pass-band. The tartrate crystal elements in accordance with this invention have high piezoelectric coupling and accordingly may be used to extend the range of crystal filters to lower frequencies than have been obtained in the past. For example, voice channels down to about 12 kilocycles per second or less may be obtained using a flexure mode tartrate crystal element, the flexure modes of motion being obtained by electrode arrangements presently used in connection with fiexure mode quartz crystal elements. The tartrate crystal elements in accordance with this invention may also be used for control of frequency modulation in oscillators. On account of the large electromechanical coupling, the frequency variation and shift may be of large value and may be controlled by an applied direct current voltage or by a suitable reactance tube, for example.

For a clearer understanding of the nature of this invention and the additional advantages, features and objects thereof, reference is made to the following description taken in connection with the accompanying drawings, in which like reference characters represent like or similar parts and in which:

Fig. 1 is a perspective view illustrating the form and growth habit in which a monoclinic crystal of ethylene diamine tartrate may crystallize, and also illustrating the relation of the surfaces of the mother crystal with respect to the mutually perpendicular X, Y and Z axes, and with respect to the crystallographic a, b and c axes;

Fig. 2 is an edge view illustrating the rectangular X, Y and Z and crystallographic a, b and 0 systems of axes for monoclinic crystals, and also illustrating the plane of the optic axes of ethylene diamine tartrate crystals;

Fig. 3 is a perspective View illustrating longitudinal mode ethylene diamine tartrate crystal elements rotated in effect to a position corresponding to a l angle in the region of 45 degrees, and a 0 angle of substantially 63 degrees or more broadly from 40 to 70 degrees;

Fig. 4 is a graph illustrating the resonance and anti-resonance frequencies and the dielectric constant characteristics of a longitudinal mode ethylene diamine tartrate crystal element as a function of temperature, and angle i being about 45 degrees and the angle 0 being about 63 degrees;

Fig. 5 is a graph illustrating the relation between the temperature at which zero temperature coefiicient of frequency occurs in longitudinal mode etheylene diamine tartrate crystal elements having a 1 angle of about 45 degrees and 0 angles varying from 40 to 68 degrees; and

Fig. 6 is aperspective view illustrating a width bending flexure mode type ethylene diamine tartrate crystal element.

This specification follows the conventional terminology, as applied to piezoelectric crystalline substances, which employs a system of three mutually perpendicular X, Y and Z axes as reference axes for defining the angular orientation of a crystal element. As used in this specification and as shown in the drawing, the Z axis corresponds to the c axis, the Y axis corresponds to the b axis, and the X axis is inclined at an angle with respect to the an axis which, in the case of ethylene diamine tartrate, is an angle of about degrees. The crystallographic a, b and c axes represent conventional terminology as used by crystallographers.

Referring to the drawing, Fig. 1 is a perspective view illustrating the general form and growth habit in which ethylene diamine tartrate may crystallize, the natural faces of the ethylene diamine tartrate mother crystal I being designated in Fig. 1 in terms of conventional terminology as used by crystallographers. For example, the top surface of the crystal body I is designated as a 001 plane, and the bottom surface thereof as aOOT plane, and other surfaces and facets thereof are as shown in Fig. 1.

The mother crystal I, as illustrated in Fig. 1, may be grown from any suitable nutrient solution by any suitable crystallizer apparatus or method, the nutrient solution used for growing the crystal I being prepared from any suitable chemical substances and the crystal I being grown from such nutrient solution in any suitable manner to obtain a mother crystal I of a size and shape that is suitable for cutting therefrom piezoelectric crystal elements in accordance with this invention. The mother crystal 1 from which the crystal elements 2 are to be cut, is relatively easy to grow in shapes and sizes that are suitable for cutting useful crystal plates or elements 2 therefrom. Such mother crystals I may be conveniently grown to sizes around two inches or more for the X, Y and Z dimensions or of any sufficient size to suit the desired size for the piezoelectric circuit elements 2 that are to be cut therefrom. It will be understood that the mother crystal I may be grown to size by any suitable crystallizer apparatus such as, for example, by a rocking tank type crystallizer or by a reciprocating rotary gyrator type crystallizer.

Crystals I comprising ethylene diamine tartrate have no water of crystallization and hence no vapor pressure, and may be put in an evacuated container without change, and may be held in temperatures as high as 100 degrees centigrade. At a temperature of about v130 degrees centigrade, some surface decomposition may start. A crystal I comprising crystalline ethylene diamine tartrate has only one cleavage plane which lies perpendicular to the Y axis. While cleavage planes may make the crystal I somewhat more difiicult to cut and process, nevertheless, satisfactory processing may be done by any suitable means such as, for example, by using an abrading belt or a sanding belt cooled by oil or by a solution of water and ethylene glycol, for example. It will be noted that the crystal elements 2 oriented in accordance with this invention have major faces which do not coincide with the cleavage plane lying perpendicularto the Y axis, and hence have mechanically stronger surfaces for mounting purposes.

Crystals I comprising ethylene diamine tartrate (CeH14N2Oa) have four dielectric constants, eight piezoelectric constants, and thirteen elastic constants, and form in the monoclinic sphenoidal class of crystals which has as its element of symmetry the b axis, the b axis being an axis of binary symmetry. As shown in Fig. 1, monocliniccrystals I comprising ethylene diamine tartrate are characterized by having two crystallographic'axes b and .c, which are disposed at right angles with respect to each other, and a third crystallographic axis a which makes an angle different than degrees from the other two crystallograp'hic axes b and c. The c axis lies along the longest direction of the unit cell of the crystalline material. The b axis is an axis of twofold or binary symmetry. In dealing with the axes and the properties of such a monoclinic crystal I, it is convenient and simpler to use a rightangled or mutually perpendicular system of X, Y and Z coordinates. Accordingly, as illustrated in Fig. 1, the method chosen for relating the conventional right-angled X, Y and Z system of axes to the .a, .b and a system of crystallographic axes of the crystallographer, is to make the Z axis coincide with the c axis and the Y axis coincide with the .b axis, and to have the X axis lie in the plane of "the a. and .c crystallographic axes at an angle with respect to the a axis, the Xaxis angle being about 15 degrees 30 minutes above the .a axis for ethylene diamine tartrate, as shown in Figs. 1 and2.

The X, Y and Z axes form a mutually perpendicular system of axes, the Y axis being a polar axis which is positive by a tension at one of its ends, as shown in Fig. 1. In order to specify which end of the Y .axisis the positive end, the plane .of the optic axes of the crystal I may be located. A monoclinic crystal I is an optically biax-ial crystal and for crystalline ethylene diamine tartrate, the planethat contains these optic axes is found to be parallel to the b or Y crystallographic axis and inclined at an angle of about 24% degrees with respect to the +Z axis, as illustrated in Fig. 2.

Fig. 2 is .a diagram illustrating the plane of the optic axes for crystals I comprising ethylene diamine tartrate. As shown in Fig. 2, the plane of the optic axes of an ethylene diamine tartrate crystal I is ,parellel to the Y or b axis, which in Fig. 2 is perpendicular to the surface of the drawing; and is inclined in a clockwise direction at an angle of about 24 /2 degrees from the +2 or -{-c crystallographic .axis. Since the +X axis lies at a counter-clockwise angle of 90 degrees from the +0 or +Z axis, and the +b +Y axis makes a right-angle system of coordinates with the .X and Z axes, the system illustrated in Fig. 2determines the positive directions of all three of the X, Y and Z axes. Hence, the positive directions of all three X, Y and Z axes may be specified with reference to the plane of the optic axes of the crystal I. A similar optical method of procedure may be used for orienting and specifying the direction of the three mutually perpendicular X, Y and Z axes of other types of monoclinic crystals. Oriented crystal cuts are usually specified in practice by known X-ray orientation procedures.

Fig. 3 is a perspective view illustrating a crystal element .2 comprising ethylene diamine tartrate that has been cut from a suitable mother crystal I as shown in Fig. 1. The crystal element2 as shown in Fig. 3 may be made into rectangular parallelepiped shape having a longest or length axis dimension L, a breadth or width axis dimension W, and a thickness or thin dimension T, the directions of the dimensions L, W and T being mutually perpendicular, and the thin or thickness axis dimension T being measured between the opposite parallel major or electrode faces of the crystal element 2. The length dimension L and the width dimension W of the crystal element 2 may be made of values to suit the desired frequency thereof. The thickness or thin dimension T may be made of a value to suit the impedance of the system in which the crystal element 2 may be utilized as a circuit element; and aiso it may be made of a suitable value to avoid nearby spurious modes of motion which, by proper dimensioning of the thickness dimension T relative to the larger length and width dimensions L and W, may be placed in a location that is relatively remote from the desired longitudinal mode of motion along the length axis dimension L.

Suitable conductive electrodes 4 and 5 may be provided adjacent the two opposite major or electrode faces of the crystal element 2 in order to apply electric field excitation thereto. The electrodes 4 and 5 when formed integral with the faces of the crystal element 2 may consist of gold, platinum, silver, aluminum or other suitable conductive material deposited upon surfaces of the crystal element 2 by evaporation in vacuum or by other suitable process. The electrodes 4 and 5 may be electrodes wholly or partially covering the major faces of the crystal element 2, and may be provided in divided or nondivided form as already known in connection with quartz crystals. Accordingly, it will be understood that the crystal element .2 disclosed in this specification may be provided with conductive electrodes or coatings 4 and 5 on their faces of any suitable composition, shape and arrangement, such as those already known in connection with Rochelle salt or quartz crystals, for example; and that they may be nodally mounted and electrically connected by any suitable means, such as, for example, by pressure type clamping pins or by one or more pairs of opposite conductive supporting spring wires 1 disposed along the nodal line 6 and cemented by conductive cement or glued to the crystal element or to the metallic coatings 4 and 5 deposited on the crystal element 2, as already known in connection with quartz, Rochelle salt and other crystals having similar or corresponding longitudinal modes of motion. Each of the supporting wires 1 may be provided with a small flatheaded end portion, the outer surface of which may be cemented directly to the major face of the crystal element 2 adjacent a node 6 thereof by a spot of any suitable adhesive cement 8. The electrical connection from each support wire 1 to the associated crystal coating 4 or 5 may be established by extending the respective conductive coating 4 or 5 onto the associated supporting Wire Z. By utilizing a good conductive cement spot 8 the electrical connection may be established directly with the associated coating or 5. Examples of support wires adapted for mounting crystal elements are illustrated in United States Patents No. 2,371,613, granted March 20, 1945, to I. E. Fair, and No. 2,275,122, granted March 3, 1942, to A. W. Ziegler, for example.

' As illustrated in Fig. .3, the thin or thickness axis dimension T of the crystal element ,2 lies in a, plane which contains the Y axis and which makes an angle I of about 45 degrees or in the region of 45 degrees with respect to the +Z axis as measured from the +Z axis. The direction of the thickness axis dimension T lying in that plane makes an angle 9 of about 63 degrees with respect to the +Y axis as measured from the +Y axis. The length axis dimension L of the crystal element 2 which is disposed normal to the thickness axis dimension T, as illustrated in Fig. 3, lies in or nearly in the plane which is determined by the Y axis and the Value of the angle a, which is in the region of 45 degrees. It will be noted that the angles I and 0 are measured in the quadrant comprising the +X, the +8? and +Z axes, the angle a being 45 degrees or in the region of 45 degrees as measured from the +Z axis toward the +X axis in the plane of the X and Z axes, and the 0 angle being in the region of 63 degrees or more broadly one of the angles from 40 to 70 degrees as measured from the +Y axis in the plane containing the Y axis, as illustrated in Fig. 3.

At the 0 angle of about 63 degrees with respect to the +Y axis, the angle e being about 45 degrees, the ethylene diamine tartrate crystal plate 2 of Fig. 3 has a zero temperature coefficient of frequency at about +27.5 degrees centigrade for its longitudinal mode of motion along the length 'axisj dimension L. At angles of 0 above and below the 0 angle of about 63 degrees referred to, the value of the temperature at which the zero temperature coefiicient of frequency occurs for the longitudinal length L mode of motion is raised or lowered from the +275 degrees centigrade value referred to, according to the angle of 0 selected, as illustrated by the curve in Fig. 5. Accordingly, the crystal element 2 of Fig. 3 may be selectively oriented for best use with the prevailing ambient temperature. The electrodes 4 and 5 disposed adjacent the major faces of the crystal element 2 provide an electric field in the direction of the thickness axis dimension T of the crystal element 2 thereby producing a useful longitudinal mode of motion along the length dimension L of the crystal element 2 with high electromechanical coupling and a low temperature coefficient of frequency over a temperature range in the region above and below about +27 degrees centigrade when the angle 0 is about 63 degrees, the angle i being about 45 degrees.

The dimensional ratio of the width dimension W with respect to the length dimension L of the crystal element 2 may be made of any suitable value in the region less than 0.7 for example, and as particularly described herein is less than about 0.5 for longitudinal length mode crystal elements 2. The smaller values of dimensional ratios of the width W with respect to the length L, as of the order of 0.5 more or less, have the effect of spacing the width W mode of motion at a frequency which is remote from the fundamental longitudinal mode of motion along the length dimension L.

I When the crystal element 2 is operated in the fundamental longitudinal mode of motion along the length dimension L thereof, the nodal line 6 occurs at the center of and transverse to the length dimension L of the crystal element 2 about mid-way between the opposite small ends thereof and the crystal element 2 may be there nodally mounted and electrically connected by any suitable means such as by one or more pairs of opposite:spring wires] cemented to .the crystal ele--- ment:2 .byyspots of cement 8 at the nodal region 6 .OfithB crystal element 2.

While the crystal element 2 is particularly described herein as being operatedv-innthe fundamental "longitudinal -mode.;. of motion; along its lengthwaxis. dimension .L, it will be understood that. it maybe operated inany even-or1odd order-,1

harmonic-thereof ina known manner bygmeans electrodes spaced along. the length L.thereof, as.

in a known manner in connection with harmonic:-

longitudinal mode :quartz crystal elements.,-. Also, if .desired,xthe crystal element. 2 may ,be operated-.-

simultaneously in the longitudinallength L and 1- dimensioncL. of. :about .1.71- centimeters, a width axis .dimensionW of about Q4269 centimeter, and-- a thickness axis-dimensionT of about.0.-1 centi width-W modes of motion by-arrangements .as disclosed, for example; in 1W. P.- Mason Patent- 2,292,885, dated .August 11, 1942;. or *simultane ously in the longitudinal :lengthL mode ofemotion and the :Wldth Weflexure mode'of motion by arrangements as disclosed; vfor example, in. MasomPatent 2,292,886.; dated August-11, 194:2;

Fig; 4 is -.a graph illustrating an." example of a thewariation, with: temperature. change, .inithe:

5 isalsoa-functionzof the dimensional ratio of the widthW with respectito the lengthgL and is lowest in value in theregion of-dimensional ratios below aboutOA.

As van-tillustrative example, the constants at aota plurality of pairs of .opposite interconnected-= temperaturewofs about .degrees centigrade of an-ethylenevdiamine.tartrate crystal plate 2 having a longitudinal-mode frequency of about 100" kilocycleseper secondga angleof about 45 degrees;.a Bangle-oi"- about-63 degreesya length axis meter; are-approximately -asfo1lows: The dielectric constant rlc=about-l 6.36 I as: expressed in" .centimeteregram-seconds units, the ratio. of capacitance r or-Cu, -C1=abOl1t 65.0, the capacitance Co..=about ,4.09.micromicrofaradsgthe xcapicitance C1=about -:1.'1'Z micromicrofarads, andlthe inductance L1=about121.7. henries;the elements C0, C1

frequencyand dielectriccharacteristics of alow-25findLllbeingifilementsill-115116convenfionaleqllivalent circuit 1 of. the electroded zcrystal. plate -2.

It. Will be noted'thatthis crystal plate 2 may have an inductancef-sufliciently comparable-with that. ofquartz-fora similar thickness '1 to enable it to be-used-as-a direct-replacement of quartz-.with-- out many changes?- Itrwill be noted that byficutting the crystal element 2 of:Fig..-.3 at!) anglervalues above and below 63 degrees, the angles? being about 45*degrees in. all-icases-,-the position-.of'thezero 'coeificient temperature may; be=--lowered below or raised above the +215 degrees centigrade value which-obtains: at a Bangle of about'63 degrees. 1 Accordingly the I crystal-element-2 iofwFig; '3 may be orientedc'for onds..(c. g. s.) units overwa.-temperatm1 use. with: the;prevailing: ambienttemperature.

from .about..90 degrees -to. +90-degrees centi-.- grade=.. Overthe .sametemperature range, the; variation in. the anti-resonance .i frequency iS-a given by the curvelabelednfx in Fig. 4,:- andsthe Fig -5 is a-graph showingia plotof the-temperature at-which the-zero temperature coefficient of frequency v ocurs in :longitudinal-mode ethylene diamineetartrate"crystal elements'z ofFig. 3,

variation jn the.resonancejrequency is given by whenlthe .or-ientation--angle 0 is variedfrom about the .curve labeled.v in; As..shown. by.- the curve in in Fig.. 4,.the resonant frequency hasa zero.tem-.. perature. coefficient. at about +27 .5 .degrees-:centi-::- grade, and from .about..0 degrees to degrees.

40 etc 70 i degrees-,:,-the angle -beingsubstantially 45 degrees -in all-=casesu As shown "by: the curve int-Fig.1; 5,1 whenthe crystal :element-2 of Fig. 3

has-a0 angle-cf aboutl63 degrees and a 1 angleentigrade th t t l, i ti in frequency i 50 of about 45 degrees,-the-temperature-atx which its small "enough for use .at all ...ordinary, ltempera-. tures. As shown .by. thecurve-fa of Fig.4, the frequency. constant. at .about.-..27. J degrees centigrade-is about..l7.1 kilocycles pensecond per centi zero temperature coefficient tof longitudinal mode frequency occurs is about +215 degrees *centigrade;.-and-when it has; a 0 angle of -about 45 degrees,-- the angle? being about 45-: degrees, the

meter of. th'e..length axis .dimensionLfor. the. temperature at/which-its zero temperature coefiie fundamental .longitudinal..mo.de of; motion along. the length axis dimension L..

It will be understood that the frequencyof the main mode of motion, which is .the fundamental.-.

cientof longitudinal, :mode: frequency occurs is about. +804: degrees centigradec. Similarly; for other angles ofce between 40 and 70 degrees, the temperature at which the zero temperature 00- longitudinal mode of motion.;.along..the..1length,r fi'lc e lloccurs f0r--cryStal..-elements12 of..Fi 3

axis dimension L, varies inversely asthe. value .of-.- the length. axis dimension L4. Thus, as -an ..ex ample. a crystal element-2 having a 5 angle. of: about 45 degrees, a .0 angle of .about..63 degrees,

a length axis dimension. L.of about one centim p a 2 O F g. 3-p ded with-two sep rate pairs of opposite electrodes 4a,, 4by5a-and 5b,

meter and a dimensional ratio of. widthl-W to;- length L of about..0.258'will have-a frequency of. about 1'71 kilocycles persecond forwitstfundae. mental longitudinal. mode. of motion along... the

will'varywith the value of the dimensionaliratiot of-width--W to length L that is selected. Atlthe. smaller valuesof dimensional ratio of widthiWi' to lengthL, as around0.3 orrless for example, the

effects or-secondary modes "of motion .upon .the l 75' mode .of,-.-.motion.;as illustrated in: Fig. 3,.. and :it

operating -.in.-.-the. =-longitudinal mode of motion:

along.- ;.the.- length-.. axis: dimensional; may be' 0b'-. tained: from" the curve of Fig. 5.

Fig. 6 is. a perspective -:-view iof the elongated instead. of ,a single pair of electrodes l and 5, in

order tooperateitinea widthflexure mode of motion at a lowerfrequency .havingat the same: length axisdimension. L.. Also, the. frequency, time. alowctemperature. coeflicient: of; frequency; Forlfrequencies below about-.40 kilocycles'per secondforexample, theisize-softhe crystaluplate 2 may become inconven-iently, largewhen-it is operated ..in., the .e straight longitudinal length may then become desirable to provide for operation in a width bending type of flexure mode of motion by providing th crystal element 2 of Fig. 3 with the divided type of integral electrodes Ga, 4b, 5a and 5b, as illustrated in Fig. 6. For this purpose, the electrodes 4a, 4b, 5a and 5b may be metal coatings similar to those shown in Fig. 3 but arranged as shown in Fig. 6, the electrode arrangement and connections being of the type described in United States Patent No, 2,259,317, granted October 14:, 1941, to W. P. Mason, for example.

The fiexure mode crystal plate 2 of Fig. 6 may comprise the ethylene diamine tartrate crystal plate 2 of Fig. 3 or other suitable longitudinal mode ethylene diamine crystal plate such as a plate cut perpendicular to the Y axis with its length axis dimension cut from O to+25 degrees with respect to the X axis, as disclosed in application Serial No. 657,886, filed March 28, 1946, by W. P. Mason, hereinbefore referred to.

While in Fig. 6 an arrangement is disclosed for operating the crystal plate 2 in the width bending mode of flexure motion, two of such crystal elements 2 may be cemented or bonded together in face-to-face relation in order to form a duplex type crystal unit for operation at a still lower frequency in a thickness bending type of fiexure motion. For this purpose, the crystal poling, electrode arrangement and electrode connections may be of the form disclosed for example in application Serial No. 477,915, filed March 4, 1943, by C. E. Lane, now United States Patent No. 2,410,825, dated November 12, 1946.

The crystal elements provided in accordance with this invention may be protected from moisture by mounting in a suitable sealed container containing dry air or evacuated, or if desired by coating the crystal surfaces with plastic films or shellac films deposited from butanol or ethanol. It will be noted that the artificial crystal bodies provided in accordance with this invention may have per se a low or zero temperature coefficient of frequency, and hence do not require an added bar of material of equal and opposite temperature coefficient of frequency secured thereto in order to obtain an overall low temperature coefiicient of frequency, as for example in the case of a half-wave 45-degree Z-cut longitudinal-mode ammonium dihydrogen phosphate crystal element which has a high negative temperature coefficient and may be cemented to a-half-wave 38 per cent nickel-62 per cent iron alloy bar having a high positive temperature coefficient in order to obtain for the wire supported composite longitudinal vibrator an overall low or zero temperature coefficient of frequency by proportioning the relative cross-sectional areas of the crystal and the metal bar.

It will be noted that among the advantageous cuts of ethylene diamine tartrate illustrated and described in this specification are orientations for which the temperature frequency coefficient may be zero at a specified temperature To, the frequency variation being sufiiciently small over ordinary temperature ranges to be useful, for example, in filter systems. The low temperature coefficient of frequency together with the high electro-mechanical coupling, the high Q, the ease of procurement, the low cost of production and the freedom from water of crystallization are advantages of interest for use as circuit elements in electrical systems generally.

Although this invention has been described and illustrated in relation to specific arrangements, it

is to be understood that it is capable of application in other organizations and is therefore not to be limited to the particular embodiments disclosed.

What is claimed is:

1. An elongated ethylene diamine tartrate piezoelectric crystal plate having its thickness or thinnest axis dimension disposed in a plane containing the Y axis and inclined at an angle of substantially 63 degrees with respect to the +Y axis as measured from the said +Y axis toward the plane of the +X and +Z axes, said plane containing said Y axis being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in said plane of said +X and +Z axes, the lengthwise or longest axis dimension of said crystal plate lying substantially in said plane containing said Y axis.

2. An elongated ethylene diamine tartrate piezoelectric crystal plate having its thickness or thinnest aXis dimension disposed in a plane containing the Y axis and inclined at one of the angles in the range from 50 to 68 degrees with respect to the +Y axis as measured from said +Y axis toward the plane of the +X and +Z axes, said plane containing said Y axis being inclined at an angle of a value not greater than substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in said plane of said +X and +Z axes, the lengthwise or longest axis dimension of said crystal plate lying substantially in said plane containing said Y axis.

3. An ethylene diamine tartrate piezoelectric crystal body of low temperature coefiicient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being made of a value corresponding to the value of said frequency and being disposed substantially in a plane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at an angle of substantially 63 degrees with respect to the +Y axis as measured from said +Y axis into the quadrant comprising the +X, +Y and +Z axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in a plane determined by said +X and +Z axes,

4. An ethylene diamine tartrate piezoelectric crystal body of low temperature coefiicient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being made of a value corresponding to the value of said frequency and being disposed substantially in a plane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at an angle of substantially 63 degrees with respect to the +Y axis as measured from said +Y axis into the quadrant comprising the +X, +Y and +Z axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in a plane determined by said +X and +2 axes, said body having a width axis dimension perpendicular to said lengthwise and thickness axes, the dimensional ratio of said width axis dimension with respect to said lengthwise axis dimension being a value less than 0.5.

aavavsa 55 An ethylenediamine" tartrate piezoelectric crystal'body of l'owtemperature coefficient of'irequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axisdimension along said major faces, said lengthwise axis dimension being disposed substantially in a-plane-containing the Y axis, said thickness axis dimension being disposed in said plane containing said-Y axis and being inclined at an angle of substantially 63 degrees with respect to the +Yaxis as measured from said +Y axis into. the" quadrant comprising the +X, +Y and -]Z axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward' said +X axis in a plane determined by said +X and -P2" axes, andmeans producing anel'ectrio'- field in the-direction of said thickness axis dimension for operating said crystal body in a mode of motion controlledby-said lengthwise axis dimension at said frequency having said low temperature coefiicient;

6. An ethylene diamine tartrate piezoelectric crystal body of low temperature coefficient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being disposed substantially in a plane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at an angle of substantially 63 degrees with respect to the +Y axis as measured from said +Y axis into the quadrant comprising the +X, +Y 'and +2 axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X aXis in a plane determined by said +X and +Z axes, said body having a width axis dimension perpendicular to said lengthwise and thickness axes, the dimensional ratio of said width axis dimension with respect to said lengthwise axis dimension being a value less than 0.5, and means producing an electric field in the direction of said thickness axis dimension for operating said crystal body in a mode of motion controlled by said lengthwise axis dimension at said frequency having said low temperature coeificient.

7. An ethylene diamine tartrate piezoelectric crystal body of low temperature coeflicient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being disposed substantially in a plane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at an angle of substantially 63 degrees with respect to the +Y axis as measured from said +Y axis into the quadrant comprising the +X, +Y and +2 axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in a plane determined by said +X and +Z axes, said body having a width axis dimension perpendicular to said lengthwise and thickness axes, the dimensional ratio of said width axis dimension with respect to said lengthwise axis dimension being a value less than 0.5, and means comprising electrodes disposed adjacent said major faces and producing an electric field in the direction of said thickness axis dimension for operating said crystal body in a longitudinal mode of motion along said lengthwise axis dimension at said frequency having said low temperature coeflicient, said lengthwise axisdimension expressed in centimeters-being a value in the region of substantially 1 7-110" divided by the'value of said frequency expressed inkilocycles per second.

82 ethylenediamine tartrate piezoelectric crystal body -'of lowtemperature coeificient of frequency' having' a thickness axis dimension perpendicul'ai-vto its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension beingmade of a value corresponding to= the value of said frequency and beingdisposed substantially in a plane containing the Y'axis, said thickness axis dimension being-"disposedin said plane containing said Y axis andbeing inclined at one of'the angles withiirtherangeof'angies from 40 to '70 degrees with respect to the +8! axis as measured from said +Y' axis into the quadrant comprising the +X, +Y" and +Z"- axes, said plane containing said Y axis being disposed intermediate said +Z axis and said +X axis;

9; An ethylene diamine tartrate piezoelectric crystal bodyof low temperature coeincient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being made of a value corresponding to the values of said frequency and being disposed substantially in a plane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at one of the angles within the range of angles from 50 to 70 degrees with respect to the +Y axis as measured from said +Y axis into the quadrant comprising the +X, +Y and +2 axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said -:-X axis in a plane determined by said +X and +2 axes, said body having a width axis dimension perpendicular to said lengthwise and thickness axes, the dimensional ratio of said width axis dimension with respect to said lengthwise axis dimension being a value less than 0.5.

10. An ethylene diamine tartrate piezoelectric crystal body of low temperature coeiilcient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being disposed substantially in a plane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at one of the angles within the range of angles from 40 to '70 degrees with respect to the +8! axis as measured from said +Y axis into the quadrant comprising the +X, +Y and +Z axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in a plane determined by said +X and +Z axes, said body having a width axis dimension perpendicular to said lengthwise and thickness axes, the dimensional ratio of said width axis dimension with respect to said lengthwise axis dimension being a value less than 0.5, and means producing an electric field in the direction of said thickness axis dimension for operating said crystal body in a mode of motion controlled by said lengthwise axis dimension at said frequency having said low temperature coefficient.

11. An ethylene diamine tartrate piezoelectric crystal body of low temperature coeflicient of frequency having a thickness axis dimension perpendicular to its major faces and a lengthwise axis dimension along said major faces, said lengthwise axis dimension being made of a value corresponding to the value of said frequency and being disposed substantially in aplane containing the Y axis, said thickness axis dimension being disposed in said plane containing said Y axis and being inclined at one of the angles within the range of angles from 50 to '70 degrees with respect to the +Y axis as measured from said +Y axis into the quadrant comprising the +X, +1 and +2 axes, said plane being inclined at an angle of substantially 45 degrees with respect to said +Z axis as measured from said +Z axis toward said +X axis in a plane determined by said +X and +2 axes, said body having a width axis dimension perpendicular to said lengthwise and thickness axes, the dimensional ratio of said width axis dimension with respect to said lengthwise axis dimension being a value less than 0.5, and means comprising electrodes disposed adjacent said major faces and producing an electric field in the direction of said thickness axis REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,292,388 Mason Aug. 11, 1942 2,303,375 Mason Dec. 1, 1942 2,309,467 Mason Jan. 26, 1943 OTHER REFERENCES Cody, Piezoelectricity, page 654, McGraW-Hill, New York,- 1946. 

